LNG Liquefaction System and Process

ABSTRACT

The present invention comprises systems and methods for natural gas liquefaction. In embodiments, the systems comprise a dual turbo-expander, methane-based refrigeration system that also uses a slip stream of LNG for additional cooling.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relies on the disclosure of and claims priority to and the benefit of the filing date of U.S. Provisional Application No. 63/340,068 filed May 10, 2022, which application is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present disclosure is directed to the field of natural gas processing, liquefaction, and storage.

SUMMARY OF THE INVENTION

Reference will now be made in detail to various exemplary implementations of the disclosure. It is to be understood that the following discussion of exemplary implementations is not intended to be limiting. Rather, the following discussion is provided to give the reader a more detailed understanding of certain aspects and features of the disclosure.

Embodiments of the invention include any of the following aspects, such as Aspect 1, which is a method for natural gas liquefaction, comprising: providing a clean gas stream and a recycled gas stream at a first pressure; mixing the clean gas stream and the recycled gas stream to form a mixed gas stream; splitting the mixed gas stream into at least a first stream and a second stream; passing the first stream and the second stream through a heat exchanger; wherein the heat exchanger cools the first stream to form a first liquefied stream by cross exchanging with one or more refrigeration streams, wherein the one or more refrigeration streams comprise: a warm expander refrigeration stream; a cold expander refrigeration stream; and a secondary refrigeration stream; and cooling the second stream by passing it through the heat exchanger to form a cooled gas stream; splitting the cooled gas stream into a first split stream and a second split stream; passing the first split stream through a warm turbo-expander to form the warm expander refrigeration stream; passing the second split stream through the heat exchanger and a cold turbo-expander to form a cooled split stream; passing the cooled split stream through a cold separator to separate the cooled split stream into a second liquefied stream and the cold expander refrigeration stream; combining the second liquefied stream with the first liquefied stream to form a third liquefied stream; passing the warm expander refrigeration stream and the cold expander refrigeration stream through the heat exchanger; wherein the warm expander refrigeration stream and the cold expander refrigeration stream are combined in or after exiting the heat exchanger to form a combined stream; generating a slipstream from the first liquefied stream; combining the slipstream with a boil off gas stream from liquid natural gas storage to form the secondary refrigeration stream; passing the secondary refrigeration stream through the heat exchanger to form a secondary refrigeration return gas stream; compressing the secondary refrigeration return gas stream using a first compressor to form a compressed secondary refrigeration return gas stream; combining the compressed secondary refrigeration return gas steam with the combined stream to form a second combined stream; compressing and cooling the second combined stream using one or more additional compressor and one or more cooler to form the recycled gas stream at pressure P_(recycle); reducing a pressure of the third liquefied stream to form a liquefied product stream; and recycling the one or more refrigeration streams through the system until a desired cryogenic liquid storage temperature is reached.

Aspect 2 is the method of Aspect 1, wherein the clean gas stream is free of impurities that tend to freeze at cryogenic temperatures.

Aspect 3 is the method of Aspect 1 or 2, wherein the first stream is a product gas stream.

Aspect 4 is the method of any of Aspects 1-3, wherein the second stream is an expander gas stream.

Aspect 5 is the method of any of Aspects 1-4, wherein the first stream is cooled by the heat exchanger to a cryogenic temperature.

Aspect 6 is the method of any of Aspects 1-5, wherein the first liquefied stream is a liquefied natural gas product.

Aspect 7 is the method of any of Aspects 1-6, wherein the cooled gas stream is a cooled expander gas stream.

Aspect 8 is the method of any of Aspects 1-7, wherein the first split stream is a warm expander split stream.

Aspect 9 is the method of any of Aspects 1-8, wherein the second split stream is a cold expander split stream.

Aspect 10 is the method of any of Aspects 1-9, wherein passing the warm refrigeration stream and the cold refrigeration stream through the heat exchanger results in cooling of other gases in the heat exchanger.

Aspect 11 is the method of any of Aspects 1-10, wherein one or more of the compressing steps is performed using work extracted at the warm turbo-expander and the cold turbo-expander.

Aspect 12 is the method of any of Aspects 1-11, further comprising monitoring one or more of flow rate, flow volume, gas temperature, gas composition, or gas pressure.

Aspect 13 is the method of any of Aspects 1-12, further comprising adjusting one or more of flow rate, flow volume, and/or flow ratio of one or more of the clean gas stream, the first stream, the second stream, the first split stream, the second split stream, the warm refrigeration stream, the cold refrigeration stream, and/or the secondary refrigeration stream based on the monitoring.

Aspect 14 is the method of any of Aspects 1-13, further comprising expanding, decreasing the pressure of, and/or cooling one or more stream by way of one or more Joule-Thompson valve(s).

Aspect 15 is the method of any of Aspects 1-14, further comprising after passing the first liquefied stream through the Joule-Thompson valve(s): providing the first liquefied stream that is an LNG to storage stream; and generating the slipstream that mixes with the boil off gas stream to form the secondary refrigeration stream.

Aspect 16 is the method of any of Aspects 1-15, further comprising delivering the liquefied product stream to a storage container once the desired cryogenic liquid storage temperature is reached.

Aspect 17 is the method of any of Aspects 1-16, wherein the warm expander, cold expander, and one or more compressor are part of a single system coupled via a bull gear and pinions.

Aspect 18 is the method of any of Aspects 1-17, wherein a single motor provides all external power required to perform the method.

Aspect 19 is the method of any of Aspects 1-18, wherein work extracted at the warm expander and the cold expander is used in recompressing the refrigeration return gas.

Aspect 20 is the method of any of Aspects 1-19, wherein the secondary refrigeration return gas stream is boosted in pressure by way of a low-pressure compressor.

Aspect 21 is the method of any of Aspects 1-20, wherein the secondary refrigeration stream passes through the heat exchanger to provide the balance of cooling for the process.

Aspect 22 is a method for natural gas liquefaction, comprising: providing a gas stream and a recycled gas stream; mixing the gas stream and the recycled gas stream to form a mixed gas stream; splitting the mixed gas stream into at least a first stream and a second stream; passing the first stream and the second stream through a heat exchanger comprising: a warm expander refrigeration stream; a cold expander refrigeration stream; and/or a secondary refrigeration stream; and wherein the heat exchanger cools the first stream to form a first liquefied stream, which is split to provide the secondary refrigeration stream and a stream of liquefied natural gas; wherein the heat exchanger cools the second stream by passing it through the heat exchanger to form a cooled gas stream, which is split into a first and second split stream: the first split stream is optionally passed through a heat exchanger and is passed through a cold turbo-expander to provide the cold expander refrigeration stream, which is optionally split to provide a second liquefied stream; and the second split stream is passed through a warm turbo-expander to provide the warm expander refrigeration stream; wherein one or more of the warm expander refrigeration stream, the cold expander refrigeration stream, and/or the secondary refrigeration stream are optionally passed through a heat exchanger and are compressed one or more times, individually or together, to provide a portion or all of the recycled gas stream.

Aspect 23 is a system for natural gas liquefaction, comprising: one or more heat exchanger comprising: a warm expander refrigeration stream; a cold expander refrigeration stream; and/or a secondary refrigeration stream; and wherein one or more of the heat exchangers comprise one or more inputs to receive one or more mixed gas streams from a natural gas stream and a recycled gas stream; wherein one or more of the heat exchangers is configured to cool the mixed gas streams and provide a first liquefied stream and a cooled gas stream therefrom; at least one warm turbo-expander configured to receive a portion of the cooled gas stream and to provide the warm expander refrigeration stream for input into one or more of the heat exchangers; at least one cold turbo-expander configured to receive another portion of the cooled gas stream and to provide the cold expander refrigeration stream for input into one or more of the heat exchangers; storage configured to receive all or a portion of the first liquefied stream, which stream optionally provides for the secondary refrigeration stream; wherein one or more of the heat exchangers comprises one or more inputs to receive one or more or all of the warm expander refrigeration stream, the cold expander refrigeration stream and/or the secondary refrigeration stream; one or more compressors with one or more inputs for receiving one or more or all of the warm expander refrigeration stream, the cold expander refrigeration stream and/or the secondary refrigeration stream, which compressors provide the recycled gas stream as an output.

Aspect 24 is a system with the components of and/or arranged/configured as shown in FIG. 1 , such as the system of Aspect 23 with the components of and/or arranged/configured as shown in FIG. 1 .

Aspect 25 is the system of Aspect 23 or 24, wherein the warm turbo-expander, cold turbo-expander, and one or more compressor are part of a single system, such as coupled via a bull gear and pinions.

Aspect 26 is a system comprising components sufficient to perform any one or more or all of the methods of Aspects 1-22.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain aspects of implementations of the present disclosure, and should not be construed as limiting. Together with the written description, the drawings serve to explain certain principles of the disclosure.

FIG. 1 is a schematic diagram of a natural gas liquefaction process according to an embodiment of the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Methods, which can be performed using such a system, are provided below. The component and stream numbering provided in the claims is made in reference to FIG. 1 . Methods using less than all of the recited steps are also included within the scope of embodiments of the invention. Methods using different combinations of the recited steps are also included. Any systems capable of operating in a manner to perform such methods are also included within the scope of the invention, as well as the exemplary system shown in FIG. 1 .

Definitions

The following terms are used throughout the disclosure. Other terms should be construed as having their ordinary meaning within the oil and gas engineering arts.

Gas Inlet Options—Clean incoming natural gas is fed into the appropriate location in the process based on inlet gas pressure. Clean gas is substantially free of H₂O, CO₂, heavy hydrocarbons (C6+), BTEX, Mercaptans, H₂S and Hg.

Recycle Compressor—A single prime mover, single shaft, multi-stage compressor. Gas from various points in the process, at different pressures, is fed into a single compressor at the suction of each stage. The inlet to the first stage is designated as low pressure (Plow). The gas entering the second stage is designated as intermediate pressure (Pint). The gas entering the third stage is designated as high pressure (P_(high)). Gas exiting the compressor is designated as Recycle pressure (P_(recycle)). Other implementations can include 2 stages, or more than 3 stages. The recycle compressor can also be implemented as a system of individual compressors each with its own prime mover or any combination thereof.

Heat Exchanger—The main heat exchanger of the refrigeration system whose function it is to cool natural gas to cryogenic temperatures. Refrigeration comes from the primary, secondary and tertiary flow paths/refrigeration streams and can be provided by a primary heat exchanger, such as a single heat exchanger (e.g., a braised aluminum heat exchanger (BAHX)), or multiple heat exchangers, such as one or more multiple passage braised aluminum heat exchanger.

Turbo Expander/Compressor—Common Shaft, high speed turbines where the turbo expander rapidly lets down gas pressure and the turbo compressor (driven by the Turbo Expander) increases gas pressure.

Mixer—A single point in the gas liquefaction systems and processes where gas streams are combined at a common pressure

Joule Thompson (JT) Valve—A special flow control valve used to rapidly expand gas (let down pressure) to provide cooling.

Liquefied Natural Gas (LNG) Storage Tank—Specialized cryogenic storage tank. LNG Storage tank can be an Isometric Container, LNG Trailer, or Stationary Tank. Storage can also be implemented as a plurality of vessels. In embodiments, the liquefied natural gas (LNG) can be stored in a buffer storage vessel before loading the LNG into subsequent storage or onto a transport truck. For example, after processing and while waiting for a transport truck to arrive, the LNG can be placed in a buffer storage for temporary storage until the truck arrives where the LNG can be loaded to the transport truck from the buffer storage, if desired.

Boil off Gas (BOG)—Natural gas in vapor phase near cryogenic liquid temperatures. Heat is always being added to the system/storage so BOG is generated as the LNG boils off to vapor. Additionally, the portion of the product stream that contains the LNG intended for storage is a two-phase stream with up to 15% vapor. The process inherently generates vapor going to the storage (e.g., buffer storage and/or an LNG transportation vehicle) which can be returned to the heat exchanger as BOG in any embodiment.

Refrigeration Streams—Provides the necessary cooling to lower the inlet natural gas temperature from close to ambient temperature to cryogenic temperatures low enough to liquify natural gas.

The term “about” in association with a numerical value means that the numerical value can vary plus or minus 10% or less of the numerical value.

The inventive dual turbo-expander, methane-based refrigeration system and method that also uses a slip stream of LNG (liquid natural gas) for additional cooling, is shown in FIG. 1 . Exemplary system components are summarized in Table 1. Various liquid and gas streams that are possible with the system and methods are described in Table 2. The numbering in Tables 1 and 2 corresponds with the reference numerals provided in FIG. 1 . The dashed flow paths in FIG. 1 provide for alternative/additional routes by which the gas and liquid streams can pass. The dashed lines between the level controllers (LC) and temperature controllers (TC) and the vales indicate control logic.

TABLE 1 Summary of System Features Reference Numeral Feature 100 Heat exchanger 200 Warm Expander Inlet Knock- Out Vessel 300 Warm Turbo-Expander 400 Cold Expander Inlet Knock- Out Vessel 500 Cold Turbo-Expander 600 Cold Separator Vessel 700 Compressor 800 Cooler 900 First Stage Compressor 1000 Second Stage Compressor 1100 Cooler 1200 Third Stage Compressor 1300 Fourth Stage Compressor 1400 Cooler 1500 LNG Storage 1600 Valve 1650 Safety Shutdown Valve 1700 Motor LC Level Controller TC Temperature Controller

TABLE 2 Descriptions of Various Streams Pressure Temperature Stream Range Range No. Stream descriptions (PSIG) (° F.) 1 Clean gas stream - preferably free of impurities that Max: 1000 Max: 120 have freezing potential at cryogenic temperatures Min: 400 Min: 40  1A Mixed gas stream - a combination of clean gas Max: 1000 Max: 120 stream 1 and recycled gas stream 26 Min: 400 Min: 40 2 First stream - mixed gas stream 1A is split into a first Max: 1000 Max: 120 stream 2 and second stream 3 Min: 400 Min: 40 3 Second stream - mixed gas stream 1A is split into a Max: 1000 Max: 120 first stream 2 and second stream 3 Min: 400 Min: 40 4 First liquefied stream - formed by passing first Max: 1000 Max: −210 stream 2 through the heat exchanger 100 Min: 400 Min: −260 5 First cooled gas stream - formed by passing second Max: 1000 Max: 20 stream 3 through the heat exchanger 100 Min: 400 Min: −20 6 Low-pressure liquefied stream - formed when the first Max: 250 Max: −210 liquefied stream 4 leaves the heat exchanger 100 at Min: 60 Min: −260 high pressure and is let down to about 70 psig to have the ability to mix the liquids from Cold Separator 600 7 Third liquefied stream - formed after slip stream 32 Max: 50 Max: −210 is split from slow-pressure liquefied stream 6 Min: 2 Min: −260 8 Liquefied product stream - formed when third Max: 50 Max: −210 liquefied stream 7 is let down to the LNG storage tank Min: 2 Min: −260 pressure. This creates a two-phase stream with mostly Liquid Natural Gas (LNG) and small amount of gas phase 9 First split stream - first cooled gas stream 5 is split Max: 1000 Max: 20 into first split stream 9 and second split stream 13 Min: 400 Min: −20 10 First gas-only stream - formed before inlet to warm Max: 1000 Max: 20 turbo-expander 300 and after any possible liquids in Min: 400 Min: −20 first split stream 9 are dropped in the Warm Expander Inlet KO (knock-out) Vessel 200 11 Warm expander refrigeration stream - Warm Turbo- Max: 250 Max: −210 Expander 300 expands the first gas-only stream 10 to Min: 60 Min: −260 a lower pressure in turn making the gas cooler 12 First warmed refrigeration stream - results after warm Max: 250 Max: 120 expander refrigeration stream 11 is routed through the Min: 60 Min: 40 heat exchanger 13 Second split stream - cooled gas stream 5 is split into Max: 1000 Max: 20 first split stream 9 and second split stream 13 Min: 400 Min: −20 14 Second cooled gas stream - formed by passing second Max: 1000 Max: −80 split stream 13 through the heat exchanger 100 Min: 400 Min: −120 15 Second gas-only stream - formed before inlet to cold Max: 1000 Max: −80 turbo-expander 500 and after any possible liquids in Min: 400 Min: −120 second cooled gas stream 14 are dropped in the Cold Expander Inlet KO (knock-out) Vessel 400 16 Two-phase stream - Cold Expander 500 expands the Max: 250 Max: −180 second gas-only stream 15 to a lower pressure in turn Min: 60 Min: −220 making the gas cooler. This is a 2-phase stream. 17 Cold expander refrigeration stream - created by Max: 250 Max: −180 separating the gas phase from two-phase stream 16 in Min: 60 Min: −220 cold separator vessel 600 18 Second liquefied stream - formed when two-phase Max: 250 Max: −180 stream 16 is separated by cold separator vessel 600 Min: 60 Min: −220 19 Second warmed refrigeration stream - formed when Max: 250 Max: 120 colder expander refrigeration stream 17 is routed Min: 60 Min: 40 through the heat exchanger 100 20 First combined stream - formed when the first and Max: 250 Max: 120 second warmed refrigeration streams (12 and 19) are Min: 60 Min: 40 combined 21 Second combined stream - first combined stream 20 Max: 250 Max: 120 and compressed secondary refrigeration return gas Min: 60 Min: 40 steam 36 are combined and this stream is routed to the suction side of the 1^(st) stage compressor 900 22 First compressed stream - formed when the second Max: 1000 Max: 350 combed stream 21 is compressed at the 1^(st) stage Min: 400 Min: 40 compressor 900 23 Second compressed stream - formed when the first Max: 1000 Max: 350 compressed stream is compressed at the 2^(nd) stage Min: 400 Min: 40 compressor 1000 24 Cooled compressed stream - formed when the second Max: 1000 Max: 120 compressed stream 23 is passed through cooler 1100 Min: 400 Min: 40 25 Third compressed stream - formed when the cooled Max: 1000 Max: 350 compressed stream 24 is compressed at the 3^(rd) stage Min: 400 Min: 40 compressor 1200 26 Recycled gas stream - formed when third compressed Max: 1000 Max: 120 stream 25 is compressed at the 4^(th) stage compressor Min: 400 Min: 40 1300 and cooled by cooler 1200 31 Boil-off gas - from the LNG Storage tank 1500 which Max: 50 Max: −210 comprises the gas phase portion of third liquefied Min: 2 Min: −260 stream 7 and any boil of gas created due to a heat leak in to the LNG Storage tanks 1500 32 Slip stream - formed from Stream low-pressure Max: 250 Max: −210 liquefied stream 6 to be routed through the heat Min: 60 Min: −260 exchanger 33 Reduced-pressure slip stream - formed when the Max: 50 Max: −210 pressure of slip stream 32 is let down to the same level Min: 2 Min: −260 as boil-off gas 31 34 Secondary refrigeration stream - formed by Max: 50 Max: −210 combining Stream “31” and Stream “33” Min: 2 Min: −260 35 Secondary refrigeration return gas stream - forms Max: 50 Max: −210 after the secondary refrigeration stream 34 is routed Min: 2 Min: −260 through the heat exchanger 100 36 Compressed secondary refrigeration return gas stream - Max: 1000 Max: 120 forms when secondary refrigeration return gas Min: 400 Min: 40 stream 35 is compressed at compressor 700 and cooled through a cooler 800

Clean gas stream 1 comprises a clean feed gas free of impurities that have freezing potential at cryogenic temperatures. Clean gas stream 1 is combined with recycled gas stream 26 to form mixed gas stream 1A. Mixed gas stream 1A is split into two streams: first stream 2, which as a warm product stream, and second stream 3, which is a warm expander gas.

First stream 2 is passed through a heat exchanger 100 which cools the gas stream to cryogenic temperatures by cross exchanging with one or more refrigeration streams, resulting in the formation of a first liquefied stream 4. The first liquefied stream 4 is at a high pressure after leaving the heat exchanger 100. The pressure of first liquefied stream 4 is reduced, resulting in low-pressure liquefied stream 6. Low-pressure liquefied stream 6 is mixed with a second liquefied stream 18, to form a third liquefied stream 7. The third liquefied stream 7 is let down to the LNG storage tank pressure. This creates a liquefied product stream 8 which is a two-phase stream with mostly Liquid Natural Gas (LNG) and small amount of gas phase. The liquefied product stream 8 is stored in LNG storage 1500.

The refrigeration streams comprise a warm expander refrigeration stream 11, a cold expander refrigeration stream 17, and a secondary refrigeration stream 34.

Second stream 3 is also passed through a heat exchanger 100 which cools the gas stream to between about −20° F. and 20° F., such as about 0° F., to form a first cooled gas stream 5. First cooled gas stream 5 is split into two streams: first split stream 9 and second split stream 13. First split stream 9 is a warm expander split stream and second split stream 13 is a cold expander split stream.

In embodiments, first split stream 9 is passed through a warm expander inlet knock-out vessel 200, which removes any liquids, resulting in a first gas-only stream 10. First gas-only stream 10 passes through a warm turbo-expander 300, which expands the stream to a lower pressure, resulting in warm expander refrigeration stream 11, which has been cooled to cryogenic temperatures through the expansion.

In embodiments, the liquid removed by knock-out vessel 200 is combined with warm expander refrigeration stream 11. Warm expander refrigeration stream 11 is then passed through the heat exchanger 100, providing refrigeration by cross-exchanging with one or more other gas streams, and resulting in first warmed refrigeration stream 12.

Second split stream 13 is passed through the heat exchanger 100 where it is where it is cooled to between −120 and −80° F., resulting in a second cooled gas stream 14. The second cooled gas stream 14 is routed through the cold expander inlet knock-out vessel 400, which removes any liquids, resulting in a second gas-only stream 15. Second gas-only stream 15 is passed through cold turbo-expander 500 to form two-phase stream 16. Two-phase stream 16 is passed through a cold separator vessel 600, which separates the two-phase stream 16 into a cold expander refrigeration stream 17 (gas) and a second liquefied stream 18. In embodiments, the liquid removed by knock-out vessel 400 is combined with two-phase stream 16 prior to passing through the cold separator vessel 600.

Colder expander refrigeration stream 17 is passed through the heat exchanger 100, thereby providing refrigeration by cross-exchanging with one or more other gas streams and resulting in second warmed refrigeration stream 19.

The first warmed refrigeration stream 12 and the second warmed refrigeration stream 19 are combined to form a first combined stream 20.

A slip stream 32 is created from low-pressure liquefied stream 6 to be routed back toward the heat exchanger. The pressure of slip stream 32 is reduced forming reduced-pressure slip stream 33, which is mixed with boil-off gas stream 31 (from the liquefied natural gas storage 1500), forming secondary refrigeration stream 34. Secondary refrigeration stream 34 is passed through heat exchanger 100 to form a secondary refrigeration return gas stream 35.

The secondary refrigeration return gas stream 35 is passed through a compressor 700 and cooler 800, forming compressed secondary refrigeration return gas stream 36. The secondary refrigeration return gas stream 36 is then combined with first combined stream 20 to form second combined stream 21. Second combined stream 21 is passed through a first stage compressor 900 forming a first compressed stream 22, which is passed through a second stage compressor 1000, forming a second compressed stream 23. The second compressed stream is cooled by cooler 1100, resulting in cooled compressed stream 24, which is further compressed by the third stage compressor 1200 forming third compressed stream 25. The third compressed stream 25 is further compressed by fourth stage compressor 1300 and cooled by cooler 1400, which results in recycled gas stream 26.

In embodiments, the system further comprises one or more valve(s) 1600. In embodiments, one or more of the valve(s) 1600 are Joule-Thomson valve(s).

In embodiments, a single motor 1700 provides all external power required to perform the method. In other embodiments, multiple motors 1700 may be used to provide required external power.

The system and process implementations shown in FIG. 1 can include one or more control valves any point in the diagrams that are capable of adjusting flow rates or ratios at any point in the system or process. Further, the drawings provided are merely intended to show exemplary implementations; other configurations not shown may also fall within the scope of the disclosure including different arrangements of features and different flow processes.

Components and features used in system and process implementations shown in the drawings and their physical implementation and arrangement can be chosen according to the judgement of an oil and gas engineer or similar artisan. Natural gas compressors can be implemented through selection of those known in the art such as those that operate by positive displacement; these include lobe, screw, liquid ring, scroll and vane type gas compressors all of which are rotary-type gas compressors, and diaphragm, double acting and single acting gas compressors all of which are reciprocating type gas compressors. Dynamic type gas compressors such as centrifugal gas compressors and axial flow gas compressors are also known. Further, compressors can be constant speed compressors or variable speed compressors. Similarly, heat exchangers such as countercurrent flow heat exchangers composed of aluminum plates and fins as well as turboexpanders/compressors useful for gas liquefaction are known and need not be detailed here. Flow processes can be implemented through any suitable pipe, such as metal piping, used for transferring natural gas such as black steel, galvanized steel, copper, brass or corrugated stainless steel tubing. Polyvinyl chloride (PVC) and polyethylene (PE) can be used for pipes buried outside a plant, which may be useful for implementing transfer to plant inlets and outlets.

Operations and processes described or depicted herein can be implemented or assisted through one or more computer processor. Implementations can include a non-transitory computer readable storage medium comprising one or more computer files comprising a set of computer-executable instructions for performing one or more of the processes and operations described herein and/or depicted in the drawings. In exemplary implementations, the files may be stored contiguously or non-contiguously on the computer-readable medium. Further, implementations include a computer program product comprising the computer files, either in the form of the computer-readable medium comprising the computer files and, optionally, made available to a consumer through packaging, or alternatively stored on cloud computing storage on one or more server and made available to a consumer through electronic distribution. As used herein, a “computer-readable medium” includes any kind of computer memory such as floppy disks, conventional hard disks, CD-ROMS, Flash ROMS, non-volatile ROM, electrically erasable programmable read-only memory (EEPROM), and RAM.

As used herein, the terms “computer-executable instructions”, “code”, “software”, “program”, “application”, “software code”, “computer readable code”, “software module”, “module” and “software program” are used interchangeably to mean software instructions that are executable by a processor. The computer-executable instructions may be organized into routines, subroutines, procedures, objects, methods, functions, or any other organization of computer-executable instructions that is known or becomes known to a skilled artisan in light of this disclosure, where the computer-executable instructions are configured to direct a computer or other data processing device to perform one or more of the specified processes and operations described herein. The computer-executable instructions may be written in any suitable programming language, non-limiting examples of which include C, C++, C #, Objective C, Swift, Ruby/Ruby on Rails, Visual Basic, Java, Python, Perl, PHP, and JavaScript.

In other implementations, files comprising the set of computer-executable instructions may be stored in computer-readable memory on a single computer or distributed across multiple computers. A skilled artisan will further appreciate, in light of this disclosure, how various implementations can include, in addition to software, using hardware or firmware. As such, as used herein, the operations can be implemented in a system comprising any combination of software, hardware, or firmware.

Implementations can include one or more computers or devices loaded with a set of the computer-executable instructions described herein. The computers or devices may be a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a particular machine, such that the one or more computers or devices are instructed and configured to carry out the processes and operations described herein. The computer or device performing the specified processes and operations may comprise at least one processing element such as a central processing unit (i.e. processor) and a form of computer-readable memory which may include random-access memory (RAM) or read-only memory (ROM). The computer-executable instructions can be embedded in computer hardware or stored in the computer-readable memory such that the computer or device may be directed to perform one or more of the processes and operations depicted in the drawings and/or described herein.

An exemplary implementation includes a single computer or device (e.g. desktop, laptop, tablet, smartphone) that may be configured at a stationary gas liquefaction plant or mobile gas liquefaction system to serve as a controller. The controller may comprise at least one processor, a form of computer-readable memory, and a set of computer-executable instructions for performing one or more of the processes and operations described and/or depicted herein. The single computer or device may be configured at a gas liquefaction plant or mobile system to serve as a controller which sends commands to motors controlling one or more Control Valves to direct or control the flow of gas including rate, volume, and direction in accordance with one or more processes and operations described herein. For example, motors controlling the Control Valves may be connected to the controller by any suitable network protocol, including TCP, IP, UDP, or ICMP, as well any suitable wired or wireless network including any local area network, Internet network, telecommunications network, Wi-Fi enabled network, or Bluetooth enabled network. The controller may be configured at the gas liquefaction plant or mobile system to control opening and closing of the Control Valves based on inputs received from one or more sensors installed within the plant or mobile system. The one or more sensors are capable of measuring or monitoring one or more gas characteristics selected from a gas pressure, temperature, flow rate, and flow volume, and can be installed in various inlets, outlets, or other conduits within the stationary plant or mobile system, or within plant or system equipment. The one or more sensors can send data to the controller through a wired or wireless connection. The controller may also allow an operator to directly control processes at the gas liquefaction plant or mobile system through opening and closing of the Control Valves through an operator interface which may be a graphical user interface (GUI) which may be presented as an HTTP webpage that may be accessed by the operator at a remote general purpose computer with a processor, computer-readable memory, and standard I/O interfaces such as a universal serial bus (USB) port and a serial port, a disk drive, a CD-ROM drive, and/or one or more user interface devices including a display, keyboard, keypad, mouse, control panel, touch screen display, microphone, etc. for interacting with the controller through the GUI.

The present invention has been described with reference to particular embodiments having various features. In light of the disclosure provided above, it will be apparent to those skilled in the art that various modifications and variations can be made in the practice of the present invention without departing from the scope or spirit of the invention. One skilled in the art will recognize that the disclosed features may be used singularly, in any combination, or omitted based on the requirements and specifications of a given application or design. When an embodiment refers to “comprising” certain features, it is to be understood that the embodiments can alternatively “consist of” or “consist essentially of” any one or more of the features. Any of the methods disclosed herein can be used with any of the systems disclosed herein or with any other systems. Likewise, any of the disclosed systems can be used with any of the methods disclosed herein or with any other methods. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention.

It is noted in particular that where a range of values is provided in this specification, each value between the upper and lower limits of that range is also specifically disclosed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range as well. The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. It is intended that the specification and examples be considered as exemplary in nature and that variations that do not depart from the essence of the invention fall within the scope of the invention. Further, all of the references cited in this disclosure are each individually incorporated by reference herein in their entireties and as such are intended to provide an efficient way of supplementing the enabling disclosure of this invention as well as provide background detailing the level of ordinary skill in the art. 

1. A method for natural gas liquefaction, comprising: providing a clean gas stream and a recycled gas stream at a first pressure; mixing the clean gas stream and the recycled gas stream to form a mixed gas stream; splitting the mixed gas stream into at least a first stream and a second stream; passing the first stream and the second stream through a heat exchanger; wherein the heat exchanger cools the first stream to form a first liquefied stream by cross exchanging with one or more refrigeration streams, wherein the one or more refrigeration streams comprise: a warm expander refrigeration stream; a cold expander refrigeration stream; and a secondary refrigeration stream; and cooling the second stream by passing it through the heat exchanger to form a cooled gas stream; splitting the cooled gas stream into a first split stream and a second split stream; passing the first split stream through a warm turbo-expander to form the warm expander refrigeration stream; passing the second split stream through the heat exchanger and a cold turbo-expander to form a cooled split stream; passing the cooled split stream through a cold separator to separate the cooled split stream into a second liquefied stream and the cold expander refrigeration stream; combining the second liquefied stream with the first liquefied stream to form a third liquefied stream; passing the warm expander refrigeration stream and the cold expander refrigeration stream through the heat exchanger; wherein the warm expander refrigeration stream and the cold expander refrigeration stream are combined in or after exiting the heat exchanger to form a combined stream; generating a slipstream from the first liquefied stream; combining the slipstream with a boil off gas stream from liquid natural gas storage to form the secondary refrigeration stream; passing the secondary refrigeration stream through the heat exchanger to form a secondary refrigeration return gas stream; compressing the secondary refrigeration return gas stream using a first compressor to form a compressed secondary refrigeration return gas stream; combining the compressed secondary refrigeration return gas steam with the combined stream to form a second combined stream; compressing and cooling the second combined stream using one or more additional compressor and one or more cooler to form the recycled gas stream at pressure P_(recycle); reducing a pressure of the third liquefied stream to form a liquefied product stream; and recycling the one or more refrigeration streams through the system until a desired cryogenic liquid storage temperature is reached.
 2. The method of claim 1, wherein the clean gas stream is free of or reduced in impurities that tend to freeze at cryogenic temperatures.
 3. The method of claim 1, wherein the first stream is a product gas stream.
 4. The method of claim 1, wherein the second stream is an expander gas stream.
 5. The method of claim 1, wherein the first stream is cooled by the heat exchanger to a cryogenic temperature.
 6. The method of claim 1, wherein the first liquefied stream is a liquefied natural gas product.
 7. The method of claim 1, wherein the cooled gas stream is a cooled expander gas stream.
 8. The method of claim 1, wherein the first split stream is a warm expander split stream.
 9. The method of claim 1, wherein the second split stream is a cold expander split stream.
 10. The method of claim 1, wherein passing the warm expander refrigeration stream and the cold expander refrigeration stream through the heat exchanger results in cooling of other gases in the heat exchanger.
 11. The method of claim 1, wherein one or more of the compressing steps is performed using work extracted at the warm turbo-expander and the cold turbo-expander.
 12. The method of claim 1, further comprising monitoring one or more of flow rate, flow volume, gas temperature, gas composition, or gas pressure.
 13. The method of claim 1, further comprising adjusting one or more of flow rate, flow volume, and/or flow ratio of one or more of the clean gas stream, the first stream, the second stream, the first split stream, the second split stream, the warm refrigeration stream, the cold refrigeration stream, and/or the secondary refrigeration stream based on the monitoring.
 14. The method of claim 1, further comprising expanding, decreasing the pressure of, and/or cooling one or more stream by way of one or more Joule-Thompson valve(s).
 15. The method of claim 1, further comprising after passing the first liquefied stream through the Joule-Thompson valve(s): i) providing the first liquefied stream that is an LNG to storage stream; and ii) generating the slipstream that mixes with the boil off gas stream to form the secondary refrigeration stream.
 16. The method of claim 1, further comprising delivering the liquefied product stream to a storage container once the desired cryogenic liquid storage temperature is reached.
 17. The method of claim 1, wherein the warm turbo-expander, cold turbo-expander, and one or more compressor are part of a single system coupled via a bull gear and pinions.
 18. The method of claim 17, wherein a single motor provides all external power required to perform the method.
 19. The method of any of claim 1, wherein work extracted at the warm turbo-expander and/or the cold turbo-expander are used in compressing the secondary refrigeration return gas stream.
 20. The method of any of claim 1, wherein the secondary refrigeration return gas stream is boosted in pressure by way of a low-pressure compressor.
 21. The method of claim 1, wherein the secondary refrigeration stream passes through the heat exchanger to provide cooling for the process.
 22. A method for natural gas liquefaction, comprising: providing a gas stream and a recycled gas stream; mixing the gas stream and the recycled gas stream to form a mixed gas stream; splitting the mixed gas stream into at least a first stream and a second stream; passing the first stream and the second stream through a heat exchanger comprising: a warm expander refrigeration stream; a cold expander refrigeration stream; and a secondary refrigeration stream; and wherein the heat exchanger cools the first stream to form a first liquefied stream, which is split to provide the secondary refrigeration stream and a stream of liquefied natural gas; wherein the heat exchanger cools the second stream by passing it through the heat exchanger to form a cooled gas stream, which is split into a first and second split stream: the first split stream is optionally passed through a heat exchanger and is passed through a cold turbo-expander to provide the cold expander refrigeration stream, which is optionally split to provide a second liquefied stream; and the second split stream is passed through a warm turbo-expander to provide the warm expander refrigeration stream; wherein one or more of the warm expander refrigeration stream, the cold expander refrigeration stream, and/or the secondary refrigeration stream are optionally passed through a heat exchanger and are compressed one or more times, individually or together, to provide a portion or all of the recycled gas stream.
 23. A system for natural gas liquefaction, comprising: one or more heat exchanger comprising: a warm expander refrigeration stream; a cold expander refrigeration stream; and/or a secondary refrigeration stream; and wherein one or more of the heat exchangers comprise one or more inputs to receive one or more mixed gas streams from a natural gas stream and a recycled gas stream; wherein one or more of the heat exchangers is configured to cool the mixed gas streams and provide a first liquefied stream and a cooled gas stream therefrom; at least one warm turbo-expander configured to receive a portion of the cooled gas stream and to provide the warm expander refrigeration stream for input into one or more of the heat exchangers; at least one cold turbo-expander configured to receive another portion of the cooled gas stream and to provide the cold expander refrigeration stream for input into one or more of the heat exchangers; storage configured to receive all or a portion of the first liquefied stream, which stream optionally provides for the secondary refrigeration stream; wherein one or more of the heat exchangers comprises one or more inputs to receive one or more or all of the warm expander refrigeration stream, the cold expander refrigeration stream and/or the secondary refrigeration stream; one or more compressors with one or more inputs for receiving one or more or all of the warm expander refrigeration stream, the cold expander refrigeration stream and/or the secondary refrigeration stream, which compressor(s) provide the recycled gas stream as an output. 